In mobile display products, the power-hunger digital core together with its lengthy strip-shaped layout orientation places stringent requirements on on-chip voltage supply rail design. The highly resistive ITOs of display driver application circuit tend to disable the effectiveness of external output capacitor for decoupling load transient. In addition, each regulator in the conventional distributed architecture introduces offset behavior due to different layout locations, which will inherit long transient response time from light to heavy loading.
FIG. 1 illustrates an electronic display panel with a conventional system of providing on-chip voltage supply. Referring to FIG. 1, a display driver IC 101 is connected to the electronic display panel 103 to drive the panel displaying images. This connection is often made by Chip-On-Glass (COG) method in mobile devices, such as mobile phones. The driver IC 101 is designed to be long and narrow in order to minimize the display panel size as shown in FIG. 1. A commonly used conducting material on the display glass is Indium Tin Oxide (ITO). ITO can be made into transparent conducting films coating on a glass substrate. ITO is commonly used for displays technologies, such as Liquid Crystal Displays (LCD), Organic Light Emitting Diodes (OLED) displays, as well as in touch panel technologies. But ITO is relatively resistive. The sheet resistance of ITO material is much higher (over 10 times) than metal connections in driver IC.
Referring to FIG. 1, digital core 105 is a collection of digital circuits in the driver IC 101 having the same power supply voltage Vdd. With an external power Vpower 109, a voltage regulator 107 in the driver IC delivers the Vdd voltage for the digital core 105. The Vpower voltage is higher than Vdd. The digital core current consumption in full operation can be several hundred mA, depending on the display panel technology, size and resolution. The VDD current is not steady. When the display is turned from off to on, the VDD current may jump from <0.1 mA up to hundreds of mA in nanoseconds. While the VDD current is fluctuating, the digital core requires a stable supply voltage Vdd in order to operate properly. An external capacitor 111 connecting to VDD via ITO is used to maintain the Vdd stability. As the current consumption increases for larger and higher resolution display panels in modern mobile electronic devices, the high resistance of the ITO connections 113 to the external capacitor 111 reduces the effectiveness in maintaining the Vdd stability. Therefore, a distributed on-chip voltage supply system with ultra-fast response is needed to address the problem.